Bone cement is used to, as the name implies, hold bone sections together. In some medical procedures, bone cement is also used to hold other devices, such as implants to bone. Bone cements consist of two primary components: a solid component, polymethyl methacrylate (PMM or PMMA), and a liquid monomer, methylmethacrylate (MMA). The solid component is typically a white powder consisting of copolymers based on the PMMs. These two components are mixed to form a polymethyl methacrylate bone cement. Liquid monomers are highly volatile. At a minimum, in the vapor state, monomers are displeasing to the nose. Monomer vapors can also irritate the skin, eyes, and respiratory tract.
Bone cement mixing and delivery systems are well known for mixing the separate components of bone cement together to form a uniform bone cement mixture and then delivering that mixture to a target site. Typically, such systems employ a mixer having a handle for manually mixing the components. Once mixed, the mixture is then manually transferred to a delivery device such as a syringe. The syringe is used to inject the mixture into the target site. Examples of target sites include medullary canals for total hip arthroplasty procedures, vertebral bodies for vertebroplasty or kyphoplasty procedures, and other sites in which bone cement is required.
Often, the types of bone cements used in these procedures have short working windows of only a few minutes thereby affecting the amount of time available for mixing and delivering the mixture to the target site. Current systems require a great deal of user interaction in set-up, including manually mixing the bone cement components and manually transferring the mixture to the delivery device. This user interaction delays delivery of the mixture to the target site, while also wasting the user's energy, which is preferably conserved to focus on the medical/surgical procedure itself. As a result, there is a need for bone cement mixing and delivery systems that are capable of quick set-up, with little user interaction.
One example of a bone cement mixing and delivery system that attempts to improve set-up time is shown in U.S. Pat. No. 5,571,282 to Earle. Earle discloses a motorized mixer that is used to mix the bone cement components. The mixer mixes the bone cement components a pre-selected amount of time, as set by the user. At the end of the pre-selected time, the mixer stops automatically and pressure is applied to the mixture to push the mixture out through a port in the bottom of the mixer to a syringe or delivery cartridge.
The release of odors and gases associated with the bone cement components can also be undesirable. As a result, there is also a need for bone cement mixing and delivery systems that are substantially self-contained such that the odors and gases associated with the bone cement components are not substantially released during mixing or transfer.
One example of a bone cement mixing and delivery system that provides such containment is shown in U.S. Pat. No. 5,193,907 to Faccioli et al. Faccioli et al. discloses an apparatus for mixing and delivering bone cement formed from liquid and powder components. The apparatus comprises a cylindrical body and a plunger slidable within the body. A powder chamber for storing the powder component is defined between the plunger and a distal end of the body. A glass ampoule storing the liquid component is disposed inside the plunger. To mix the components, a user presses a plug in the plunger's proximal end downwardly to urge a tip of the glass ampoule against a cammed surface (or against a shattering assembly) to release the liquid component. The liquid component then passes through a filter mounted to a head of the plunger and out channels defined through the head to enter the powder chamber. The liquid and powder components are mixed by shaking the body to form the bone cement mixture. After mixing, the plunger is used to press the bone cement mixture out of a distal aperture in the body and through a flexible conduit to a target site.
Other ways in which the prior art attempts to contain the odors and gases associated with the bone cement components is to contain the liquid component, usually the most noxious, within a self-contained handling unit that provides a barrier between the user and a monomer of the liquid component. An example of this type of unit is shown in U.S. Pat. No. 7,073,936 to Jonsson. Jonsson discloses an inner container enclosing a glass ampoule containing a liquid monomer of bone cement and a device for breaking the glass ampoule so that its contents can be sucked into a mixing vessel under partial vacuum. The device for opening the ampoule includes a threadable cap for pushing downward on the ampoule.
The prior art also attempts to prevent release of the monomer and its vapors by using a cover. One device uses a needle protector positioned over a needle. Another assembly uses a sealing plug positioned over a needle. In both cases, the cover prevents the release of the monomer and its vapors prior to removal of the cover. However, once removed, the monomer and its vapors can still be inadvertently dripped or otherwise released prior to use.
The prior art also relies on either breaking or piercing the ampoule to release the monomer contained within the ampoule. Some assemblies rely on pushing the ampoule against an inclined surface to break the ampoule along a weak point. Other assemblies rely on pushing a single cutting point or needle against the ampoule to pierce the ampoule. This can result in less than the entire contents of the ampoule being released and mixing with the powder.